It has been known since 1937 that useful polymers can be made from the poly-addition reaction of isocyanates with glycols and diamines. Such polymers are now fabricated in many forms including elastomers, fibers, coatings, adhesives and rigid and flexible foams.
Cast elastomers are produced by conducting the necessary chemical reactions in a mold. Urethane cast elastomers are used in tires, grain chute liners, conveyer belts and in many other uses. It is known to use amines such as 4,4'-methylenebis(2-chloroaniline) as a chain extender in this process; see for example, U.S. Pat. No. 3,752,790. Presently, the use of this chain extender is not favored because of its toxicological properties.
The basic principles of the RIM (reaction injection molding) process were developed in Germany by Bayer AG. At first, these investigations were directed toward production of high density, integral skin, rigid foams. Later, the studies evolved into investigation of the preparation of automative parts by the RIM process. Typically this process has been used to produce elastomeric urethanes in molded parts used in production of fascia for front and rear ends of automobiles. Some amines have been suggested for use as chain extenders in RIM; it has also been suggested that butanediol be used as a chain extender, Prepelka, D. J. et al, Advances in Reaction Injecting Molding, pages 132-165, (1975) in Advances in Urethane Science Technology.
It has previously been suggested that the addition of certain alkyl substituted hydroxy aryl compounds to polyurethane compositions which are the reaction products of a polyester or polyether glycol and a polyisocyanate tend to stabilize the polyurethane compositions against degradation by heat and light. For example, U.S. Pat. No. 2,915,496 discloses the addition of alkyl substituted hydroxy aryl compounds having an alkyl group of at least 3 carbon atoms located at a position ortho to each hydroxy group to polyurethane compositions which are the reaction products of long chain polyethers and polyisocyanates to retard or resist degradation of the compositions caused by exposure to oxygen or ozone. Reportedly, the life of polyether-urethane foams have been increased many times by the use of such antioxidants which cannot react with the isocyanate compounds of the polyurethane compositions.
U.S. Pat. No. 3,385,820 discloses the stabilization of thermoplastic polyalkyleneether polyurethanes and polyurethaneamides against heat- and light-induced degradation by the incorporation therein of a synergistic combination of certain phenolic stabilizers used in particular concentrations. The phenolic antioxidants are a mixture of (A) 4,4'-butylidenebis-(2-t-butyl-5-methylphenol) and (B) 2,2'-methylenebis-(4-methyl-6-t-butylphenol) with the proviso that the weight ratio of (A) to (B) present is in the range of 2:1 to 9:1.
U.S. Pat. No. 4,203,889 discloses at column 4, lines 29-36 several known hindered phenolic antioxidants commonly used to reduce the deterioration of polyurethane compositions due to nitrogen oxide fumes. Included are 2,6-di-t-butylphenol, 2,6-di-t-butyl-p-cresol, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-butylidenebis(6-t-butyl-m-cresol), 4,4'-methylenebis(2,6-di-t-butylphenol), 4,4'-thiobis(6-t-butyl-o-cresol), 4,4'-thiobis(6-t-butyl-m-cresol), styrenated phenols and styrenated cresols, such as Wingstay S, and the like.
U.S. Pat. No. 3,573,251 discloses the addition of certain substituted phenols in combination with certain organic phosphites to polyurethane elastomers to render them resistant to discoloration on exposure to atmospheric fumes and ultraviolet radiation. Typically substituted phenols have the formulae: ##STR1## where R.sub.1 is hydrogen or alkyl (C.sub.1 -C.sub.8); R.sub.2 is alkyl (C.sub.4 -C.sub.8); and R.sub.3 and R.sub.4 are alkyl (C.sub.1 -C.sub.8). Typical organic phosphites have the formulas: ##STR2## where R' are R" are alkyl (C.sub.6 -C.sub.18); X is oxygen or sulfur; Q is a hydrogenated bisphenol A residue; and x is sufficient to provide a molecular weight of at least 1,000.
U.S. Pat. No. 3,085,991 discloses the addition of monosubstituted phenols which may be grouped into the classes consisting of monoalkyl ethers of dihydroxybenzene, alkyl or alkylated phenols, chloro or chlorinated phenols and the nitro phenols to stabilize or prevent uncontrolled post curing of freshly prepared polyurethane gum stock without the necessity for sheeting and treating the sheeted material to effect stabilization.
U.S. Pat. No. 3,706,680 discloses foamed polyurethanes prepared from diphenols and polyisocyanates. The diphenols are compounds having the general formula: ##STR3## wherein R is an alkylidene radical, containing from 1 to about 8 carbon atoms, ##STR4## X is halogen, or an alkyl radical, preferably having from 1 to 12 carbon atoms and n is a positive integer from 0 to 3.
The diphenol starting materials are preferably 4,4'-isopropylidene diphenols having the general formula: ##STR5## wherein R, R.sub.1, R.sub.2, and R.sub.3 are independently selected from the group consisting of hydrogen, chlorine, bromine, and alkyl radicals having from 1 to 12 carbon atoms.
Applicants have now discovered that polyurethanes can be produced using dihydroxyaromatic compounds as chain extenders. Preferred polyurethanes of this type are RIM molded products or cast elastomers.
Thus, the compositions of this invention include a polyurethane which is the reaction product of an organic polyisocyanate with:
(a) an aliphatic polyhydroxy compound having two or more aliphatic hydroxy groups and a molecular weight within the range of from about 400 to about 7000, and PA1 (b) an aromatic chain extender having two aromatic hydroxy groups each containing a reactive hydrogen, which is either a liquid or is soluble in said aliphatic polyhydroxy compound at a reaction temperature employed to produce said polyurethane; PA1 I. dihydroxybenzenes and alkyl-substituted dihydroxybenzenes, wherein the alkyl groups have up to about 6 carbon atoms and the total number of carbon atoms in the alkyl groups in said alkyl-substituted dihydroxybenzene is up to about 12 carbon atoms, and PA1 II. alkylene bridged, alkyl-substituted bisphenols wherein the alkylene bridge contains up to about 6 carbon atoms and the total number of carbon atoms in the alkyl groups attached to each benzenoid nucleus is at least one but does not exceed about 12; PA1 (i) Compositions of matter which are products obtained by the use of the dihydroxybenzenes of the type defined herein as chain extenders for the urethane reaction. These compositions include the polyurethane products per se, as well as the articles made therefrom. Further; these compositions include the various mixtures of the dihydroxybenzenes and other urethane-forming substances used in the formation of the polyurethane polymers of this invention. Such mixtures include, for example, a mixture injected into the mold for the RIM process, which mixture comprises a dihydroxybenzene chain extender of this invention with the other chemical substances used to prepare the RIM-produced part. PA1 (i) at a temperature within the range of about 15.degree. C. to about 100.degree. C. subjecting to static impingement mixing PA1 (ii) subsequently injecting a shot of said preproduct at said temperature into a closed preheated mold having a temperature of from about 15.degree. C. to about 100.degree. C., PA1 (iii) opening the mold and removing the formed polyurethane molded product, and PA1 (iv) optionally subjecting said molded product to a postcure at a temperature within the range of from about 50.degree. C. to about 150.degree. C.; said process being conducted such that the amount of dihydroxyaromatic compound is from about 5 to about 30 weight percent of the total weight of components (a)-(d) and such that there is a substantially stoichiometric ratio of isocyanate groups on the one hand and the total of hydroxy groups in said aliphatic polyhydroxy compound and said dihydroxyaromatic chain extender on the other. PA1 (a) at a temperature of about 25.degree. C. to about 150.degree. C. forming a prepolymer by reacting (i) an organic polyisocyanate and (ii) an aliphatic polyhydroxy compound having two or more aliphatic hydroxy groups and a molecular weight of about 400 to about 7000, subsequently PA1 (b) at a temperature of from about 80.degree. C. to about 150.degree. C. reacting with said prepolymer thereby produced a dihydroxyaromatic chain extender selected from PA1 I. dihydroxybenzenes and alkyl-substituted dihydroxybenzenes wherein the alkyl groups have up to about 6 carbon atoms and the total number of carbon atoms in the alkyl groups in said alkyl-substituted dihydroxybenzene is up to about 12 carbon atoms, and PA1 II. alkylene bridged, alkyl-substituted bisphenols wherein the alkylene bridge contains up to about 6 carbon atoms and the total number of carbon atoms in the alkyl groups attached to each benezenoid nucleus is at least two but does not exceed about 12; PA1 (c) said process being conducted such that the amount of dihydroxyaromatic compound is from about 5 to about 30 weight percent of the total weight of said dihydroxyaromatic compound and components (i) and (ii) and such that there is a substantially stoichiometric ratio of isocyanate groups on the one hand and the total of hydroxy groups in said aliphatic dihydroxy compound and said dihydroxyaromatic chain extender on the other.
the amount of said dihydroxyaromatic chain extender being from about 5 to about 30 weight percent of the total weight of said aromatic chain extender, aliphatic polyhydroxy compound and polyisocyanate; the amount of said aliphatic polyhydroxy compound being such that there is a substantially stoichiometric ratio of isocyanate groups on the one hand and the total of hydroxy groups in said aliphatic polyhydroxy compound and said chain extender on the other hand; said dihydroxyaromatic chain extender being selected from
said dihydroxyaromatic chain extenders being further characterized by having no more than one tert-alkyl group on a position adjacent to any hydroxy group.